Her husband, the Duke of York, was the leading contender for the House of York's claim to the throne of England. York was made Lord Protector of England in 1453 and 1455, however he did not press his claim to the throne during these two periods.[2] In 1460, York was named Prince of Wales and again Lord Protector of the Realm.[3] With King Henry VI in custody, the Duke of York became the de facto ruler of England. However, before York could claim his crown, he was defeated and killed in December 1460 at the Battle of Wakefield with his son, Edmund of York, and his brother-in-law the Earl of Salisbury. The Duchess of York narrowly missed becoming queen consort of England and her son, Edward, Earl of March, was crowned in March 1461.[4] However, in 1477, following the marriage of her grandson Richard of York, the Duchess was accorded the title Queen of right after using the title of Cecily, the king's mother and late wife unto Richard in right king of England and of France and lord of Ireland since 1464.[5]

In 1424, when Cecily was nine years old, she was betrothed by her father to his thirteen-year-old ward, Richard Plantagenet, 3rd Duke of York. Ralph Neville died in October 1425, bequeathing the wardship of Richard to his widow, Joan Beaufort. Cecily and Richard were married by October 1429. Their daughter Anne was born in August 1439 in Northamptonshire. When Richard became a king's lieutenant and governor general of France in 1441 and moved to Rouen, Cecily moved with him. Their son Henry was born in February but died soon after.

Their next son, and the future King, Edward IV was born in Rouen on 28 April 1442 and immediately baptised privately in a small side chapel. He would later be accused of illegitimacy directly by his cousin, Richard Neville, 16th Earl of Warwick, and by his own brother, George, Duke of Clarence; this was a common method of discrediting political enemies, and George and Warwick were in dispute with Edward at the time and seeking to overthrow him. The claims would later be dismissed. Nonetheless, some modern historians give serious consideration to the question, and use Edward's date of birth as supporting evidence: assuming Edward was not premature (there being no evidence either way), Richard of York would been several days march from Cecily at the time of conception and the baby's baptism was a simple and private affair (unlike that of his younger brother, Edmund, which was public and lavish). This is countered by other historians, however, who point out that Cecily's husband could easily, by the military conventions of the time, have returned briefly to Rouen, where Cecily was living at the time, whilst baptism conventions of the time meant that a low-key baptism would be more likely due to Richard of York's political standing at the time vis-a-vis his later position, and fears for the baby's survival; if the difference in baptisms was to be taken as a disavowal of an otherwise acknowledged and cherished heir, it would not only be a humiliation of a wife Richard otherwise valued before and after Edward's birth, but also a personal and political humiliation. In any case, Richard acknowledged the baby as his own, which established legal paternity.

After the outbreak of the Wars of the Roses, Cecily remained at their home, Ludlow Castle, even when Richard fled to Ireland and Continental Europe. At the same time she surreptitiously worked for the cause of the House of York. When a parliament began to debate the fate of the Duke of York and his supporters in November 1459, Cecily travelled to London to plead for her husband. One contemporary commentator stated that she had reputedly convinced the king to promise a pardon if the Duke would appear in the parliament in eight days. This failed and Richard's lands were confiscated, but Cecily managed to gain an annual grant of £600 to support her and her children.

After the Yorkist victory at the Battle of Northampton in July 1460, Cecily moved to London with her children and lived with John Paston. She carried the royal arms before Richard in triumph in London in September. When the Duke of York and his heirs officially recognised as Henry VI's successors in the Act of Accord, Cecily became a queen-in-waiting and even received a copy of the English chronicle from the chronicler John Hardyng.

Her eldest son Edward successfully continued the fight against the Lancastrians. When Cecily moved to Baynard's Castle in London, it became the Yorkist headquarters and when Edward defeated the Lancastrians, she became an effective Queen Mother.

During the beginning of Edward's reign, Cecily appeared beside him and maintained her influence. In 1461 she revised her coat of arms to include the royal arms of England, hinting that her husband had been a rightful king. When Edward married Elizabeth Woodville, he built new queen's quarters for her and let his mother remain in the queen's quarters in which she had been living.

In 1469, her nephew, the Earl of Warwick, father-in-law of her sons George and Richard, rebelled against Edward IV. Warwick also began to spread rumours that the king was a bastard and that his true father was not the Duke of York but an archer named Blaybourne at Rouen, evidence of which has been assembled.[6] By some interpretations, that would have meant that Clarence was the rightful king. Warwick had earlier made similar accusations against Margaret of Anjou. Cecily said little about the matter in public, despite the fact that she had been accused of adultery. She visited Sandwich, possibly trying to reconcile the parties. When the rebellion failed the first time, she invited Edward and George to London to reconcile them. Peace did not last long and in the forthcoming war she still tried to make peace between her sons.

Edward IV was briefly overthrown by Warwick and Margaret of Anjou, and for about six months (October 1470 – April 1471) Henry VI was restored to the throne. The breach between Edward and his brother George was apparently never really healed, for George was executed for treason in the Tower of London on 18 February 1478. Edward IV died suddenly on 9 April 1483, leaving two sons aged 13 and 10. Cecily Neville's youngest son Richard, their uncle, was appointed their protector by Edward's will, but he had them placed in the Tower, whence they were never to emerge; their subsequent fate is a matter of dispute. A subsequent 'enquiry' found that that Edward IV's marriage to Elizabeth Woodville had been invalid: their children were thus pronounced illegitimate, making Richard the legal heir to the crown. The Princes in the Tower were declared illegitimate by Act of Parliament in 1483 to allow their uncle Richard to be crowned Richard III on 6 July 1483.

Richard's reign was brief, as he was defeated and killed on 22 August 1485 at the Battle of Bosworth by the last Lancastrian, Henry Tudor. Thus by 1485, Cecily's husband and four sons had all died, although two of her daughters, Elizabeth and Margaret, still lived. On 18 January 1486, Cecily's granddaughter, Elizabeth of York, eldest daughter of Edward IV, married Henry VII and became Queen of England. Cecily devoted herself to religious duties and her reputation for piety comes from this period.

Duchess Cecily died on 31 May 1495 and was buried in the tomb with her husband Richard and their son Edmund at the Church of St Mary and All Saints, Fotheringhay, Northamptonshire, with a papal indulgence. All subsequent English monarchs, beginning with Henry VIII, are descendants of Elizabeth of York, and therefore of Cecily Neville.

"Cecill wif unto the right noble Prince Richard late Duke of Yorke" made her will on 1 April 1495. It was proved at the Prerogative Court of Canterbury on 27 August of the same year.[8]

As the daughter of Ralph Neville, 1st Earl of Westmorland, Cecily inherited Westmorland's arms which were impaled with that of the Duke of York's. The Duke of York inherited the associated arms of his grandfather, Edmund of Langley, son of King Edward III; Quarterly, 1st and 4th, France modern, 2nd and 3rd England, with a label of three points Argent each point charged with three torteaux Gules.[9] In 1461, Cecily changed her arms to include the Royal coat of arms of England to imply that her late husband had been the rightful king.[5]

Cecily Neville as the Duchess of York is a principal character in Shakespeare's play The Tragedy of King Richard III. She is portrayed as having deep affection for her dead sons George and Edward, but is cold and unloving to Richard, who she refers to as a "false glass that grieves me when I see my shame in him." Because Richard is depicted as a hunchback – he suffered from scoliosis, not kyphosis – the Duchess seems to hate him for his deformity and for his difficult birth, which several characters in the play gossip about. After Richard has done away with The Princes in the Tower, his mother turns against him completely, cursing him with the damning words: "Bloody thou art, Bloody will be thy end!" She has been portrayed by many noted actresses, including Elinor Aickin, Eleanor Bron, Annette Crosbie (for BBC Shakespeare in 1983), Helen Haye (in Laurence Olivier's 1955 film), Anne Jeffreys, and, in the 1995 film starring Ian McKellen, Dame Maggie Smith. In this last version, her character was given several scenes belonging to Margaret of Anjou in the actual play. In the 1955 Olivier film, her role was reduced to little more than a bit part.

In 2013, the Duchess is portrayed by Caroline Goodall in the television series The White Queen; a series based on three of the novels from the Cousins' War series by author Philippa Gregory. In episode one, Lady Cecily's first scene is an exchange with Jacquetta of Luxembourg and her daughter, Elizabeth Woodville. In this meeting, Jacquetta, as her daughter's mouthpiece, really oversteps the historical mark. The disapproving Duchess, who was known in real life as "proud Cis," is too easily overcome by her social inferiors when they whip out her apparent "secret" affair with a French archer and Elizabeth commands that she bow before her. Lost for words, she is silenced within minutes, almost cowed by them. While contemporary notions of "courtesy" dictated extreme forms of submission to the queen, this is a Lady Cecily straight from the pages of a novel rather than the actual proud aristocrat who asserted her own right to rule.[11]